1. Field of the Invention
The invention relates to an electronic communication system for a vehicle, including a base station which is accommodated in the vehicle and at least one portable data carrier which is arranged to exchange data signals with the base station.
2. Description of the Related Art
Communication systems of this kind serve notably for controlling the entry to the vehicle. Systems of the kind set forth are known as “keyless central locking systems” or “keyless go-inhibit systems”. Such a system is described in the article “Türsteher ohne Bodyguard-Format” by Dr. Stephan Schmitz and Jasek Kruppa, published in the magazine “Elektronik”, Vol. 22, 1998, pp. 148 to 156.
The cited publication discloses a keyless central locking system for use in vehicles which includes the following components:    a transponder which can be embedded in a chip card or in a key grip and may be provided with an antenna coil, a battery, a UHF transmitter and pushbuttons,    an LF antenna in the mirror on the driver's door,    an UHF receiver in the vehicle which is activated as soon as it receives (deliberately triggered by the user) an appropriate UHF sequence from the transponder,    a mechanical switch in the door handle for activating a passive entry system, including an additional pushbutton for initiating the locking procedure, the base station or the door module and a control device.The transponder transmits data signals to the vehicle via a UHF link, whereas the transmission from the vehicle to the transponder always takes place via an LF signal of a frequency of 125 kHz. If desired, the transmission from the transponder to a vehicle can also be realized by means of such an LF signal.
A keyless locking system of this kind is capable of simplifying the opening of a vehicle to some extent in comparison with the use of a mechanical door key. However, such simplification is limited by the fact that the user must still find and operate the transponder as before. Thus, the problem remains that the transponder must always be carried in a pocket or the like and that it must be retrieved therefrom in order to operate it. It is also to be noted that even this minor advantage is not achieved for the go-inhibit function, i.e. for the starting of the vehicle.